Important Parts of a Rolex Watch: The Rolex Case

Welcome to the next chapter of our Important Parts of a Rolex Watch series where we’re studying each component of a Rolex in great detail. Following our in-depth look at the movements that power Rolex watches, we’re now turning our attention to the part that not only protects the movement but is arguably the most important design element of the watch: the Rolex case.

The History of the Rolex Oyster Case

In 1926, Rolex made history by inventing the world’s first waterproof watch case the company dubbed the Oyster. In fact, just one year later, the waterproofness of the Rolex Oyster was put to the test when it accompanied Mercedes Gleitze during her swim across the English Channel in 1927. After 10 hours in the water, the Rolex Oyster continued to perform perfectly!

Over the years, improving the water resistance of the Oyster case has continued to be a focus for Rolex. Today, all Oyster Perpetual watches (the broad label given most Rolex watches aside from Cellini watches) have a minimum water resistance of 100 meters. However, as expected, Rolex dive watches have much high water resistance ratings: Submariner 300 meters; Sea-Dweller 1,220 meters; Deepsea 3,900 meters.

Important Components of a Rolex Case

So, how does Rolex guarantee the water resistance of their Oyster cases? It’s all thanks to the case structure they patented back in 1926 that involves screwing down the bezel, winding crown, and caseback to the middle case.

A solid middle case: the center section of the Rolex Oyster case is stamped and machined from a solid block of metal (either steel, gold, or platinum depending on the model). This makes up backbone of the watch case to which all the other components are attached to.

Screw-down fluted caseback: The caseback of the Oyster case is solid, screwed-down, and fluted. This is to ensure that the case is hermetically sealed with no risk of water seeping into the movement. Rolex does not make transparent casebacks for any of their Oyster watches.

Crystal and bezel: The crystal that protects the dial is mounted on a gasket then the bezel is screwed down on top, ensuring an airtight seal. Previous crystals were made of acrylic while today’s crystals are all sapphire. Since 1953, most Rolex watches with a date function include a Cyclops magnification lens above the date except for discontinued versions of the Sea-Dweller and all versions of the Deepsea.

Screw-down winding crown: Rolex patented a waterproof winding crown in 1926, which was fitted with a metal gasket that would screw into a tube placed on the interior of the watch case. In 1953, Rolex debuted the Twinlock winding crown (fitted with two synthetic O-ring gaskets instead of one metal one) on the then-new Submariner to increase water resistance. In 1970, Rolex debuted the Triplock winding crown (with three O-ring gaskets) on the Sea-Dweller. Today, depending on the model, all Rolex Oyster cases are fitted with either a Twinlock or a Triplock winding crown.

Helium Escape Valve: In 1967, Rolex developed and patented the Helium Escape Valve to allow excess pressure built up in the watch to escape during post—saturation-diving decompression periods. The Sea-Dweller and Deepsea Rolex dive watches are fitted with helium escape valves.

Rolex Case Material Options

Rolex case material options include a variety of metals including stainless steel, gold, and 950 platinum. However, this being Rolex, there are some notable points to consider.

First of all, in 1985, Rolex was the first watchmaker to use 904L stainless steel (a superalloy that boasts anti-corrosion properties an offers exceptional sheen) for the cases of all its steel watches—moving away from the industry standard 316L stainless steel. As of 2018, Rolex began referring to the steel they use on their watches as Oystersteel.

Furthermore, Rolex currently produces all of its own 18k gold at an in-house foundry to ensure exceptional quality control. Plus, in 2005, Rolex developed and patented a rose gold alloy they call Everose, which promises to never fade.

Other Rolex terms to keep in mind when referring to case materials include Rolesor, (the combination of gold and steel on the same watch) and Rolesium (the combination of platinum and steel on the same watch).

Rolex Case Size Quick Guide

Over the course of Rolex’s history, the company has offered a wide variety of case sizes—even within the same watch collection. Here’s a quick Rolex case size guide.

Rolex Oyster Perpetual Case Sizes

Model	Circa	Case Size
Oyster Perpetual	1931 – Present	34 mm
Oyster Perpetual	1959 – Present	36 mm
Ladies’ Oyster Perpetual	1964 – 2000s	24 mm
Midsize Oyster Perpetual	1960s – Present	31 mm
Oyster Perpetual 26	2014 – Present	26 mm
Oyster Perpetual 39	2015 – Present	39 mm

Rolex Air-King Case Sizes

Model	Circa	Case Size
Air-King	1945 – 2016	34 mm
Air-King Date	1958 – 1980s	35 mm
Air-King	2016 – Present	40 mm

Rolex Datejust Case Sizes

Model	Circa	Case Size
Men’s Datejust 36	1945 – Present	36 mm
Men’s Datejust Oysterquartz	1977 – 2000s	36 mm
Men’s Datejust II	2009 – 2016	41 mm
Men’s Datejust 41	2016 – Present	41 mm
Midsize Datejust	1960s – Present	31 mm
Lady-Datejust 26	1957 – 2015	26 mm
Lady-Datejust 28	2015 – Present	28 mm

Rolex Date Case Sizes

Model	Circa	Case Size
Men’s Date	1950s – Present	34 mm
Midsize Date	1960s – 1980s	31 mm
Ladies’ Date	1960s – 2000s	26 mm

Rolex Explorer Case Sizes

Model	Circa	Case Size
Explorer	1953 – 2010	36 mm
Explorer 39	2010 – Present	39 mm

Rolex Submariner Case Sizes

Model	Circa	Case Size
Submariner	1953 – 1959	38 mm
Submariner	1959 – 2021	40 mm
Submariner Date	1966 – 2021	40 mm

Rolex GMT-Master / GMT-Master II Case Sizes

Model	Circa	Case Size
GMT-Master	1955 – 1959	38 mm
GMT-Master	1959 – 1999	40 mm
GMT-Master II	1983 – Present	40 mm

Rolex Day-Date “President” Case Sizes

Model	Circa	Case Size
Day-Date 36	1945 – Present	36 mm
Day-Date Oysterquartz	1977 – 2000s	36 mm
Day-Date Masterpiece	2000 – 2015	39 mm
Day-Date II	2009 – 2016	41 mm
Day-Date 40	2016 – Present	40 mm

Rolex Milgauss Case Sizes

Model	Circa	Case Size
Milgauss	1956 – 1988	38 mm
Milgauss	2007 – Present	40 mm

Rolex Daytona Case Sizes

Model	Circa	Case Size
Daytona (Manual-Wound)	1963 – 1988	38 mm
Daytona (Automatic)	1988 – Present	40 mm

Rolex Sea-Dweller Case Sizes

Model	Circa	Case Size
Sea-Dweller	1967 – 2009	40 mm
Sea-Dweller Deepsea	2008 – Present	44 mm
Sea-Dweller	2014 – 2017	40 mm
Sea-Dweller	2017 – Present	43 mm

Rolex Explorer II Case Sizes

Model	Circa	Case Size
Explorer II	1971 – 1985	39 mm
Explorer II	1985 – 2011	40 mm
Explorer II	2011 – Present	42 mm

Rolex Pearlmaster Case Sizes

Model	Circa	Case Size
Pearlmaster	1992 – 2015	29 mm
Pearlmaster 34	2000 – Present	34 mm
Pearlmaster 39	2015 – Present	39 mm

Rolex Yacht-Master Case Sizes

Model	Circa	Case Size
Yacht-Master 40	1992 – Present	40 mm
Midsize Yacht-Master	1994 – 2016	35 mm
Ladies’ Yacht-Master	1994 – 2012	29 mm
Yacht-Master 37	2016 – Present	37 mm

Rolex Yacht-Master II Case Sizes

Model	Circa	Case Size
Yacht-Master II	2007 – Present	44 mm

Rolex Sky-Dweller Case Sizes

Model	Circa	Case Size
Sky-Dweller	2012 – Present	42 mm

— Featured Photo and Body Photo Credits: BeckerTime’s Archive.